So your DVD player seems to be unable to play Xvid encoded videos.
Xvid is a free codec (kind of underground), contrary to Divx, for which you have to pay and which is legitimate.
Either you can update the firmware of your DVD player to be able to read Xvid .avi files, or you need to convert them to Divx encoded videos.
You should be able to do this by downloading the free Divx codec and using MPEG Streamclip as the application to do the actual transcoding.